Physicochemical characterization of alpha-crystallins from bovine lenses: hydrodynamic and conformational properties

A detailed investigation of hydrodynamic and conformational behavior has been made of the HM-crystallin and -crystallins of bovine lens. Results from this study indicated that HM (high-molecular-weight -crystallin) and (low-molecular-weight -crystallin) possess considerable size and charge heterogeneities in their native structures and subunit polypeptides, respectively. Sedimentation velocity showed a heterogeneous polydisperse system of HM with an average sedimentation coefficient of about 50 S and a more homogeneous system of -crystallin of 20 S. Viscosity and circular dichroism studies pointed to a compact and globular shape of dominant -sheet conformation for -crystallin, yet a highly asymmetrical and aggregated form for HM. The conformational stability of -crystallin was investigated in the presence of various denaturants. The evidence presented shows that hydrogen bonding is the main force in maintaining the quaternary structure of compact native -crystallin. Conformational flexibility of -crystallin demonstrated in the equilibrium unfolding study indicated a multistep transition that made the extraction of thermodynamic data from the heat denaturation study difficult. Temperature perturbation on -crystallin suggested the possible involvement of hydrophobic interaction in the aggregation process, leading to the formation of HM from -crystallin. The comparison of conformational properties between HM and -crystallin strongly indicated that HM is a denatured form of -crystallin.     

A review of modern approaches to the hydrodynamic characterisation of polydisperse macromolecular systems in biotechnology

This short review considers the range of modern techniques for the hydrodynamic characterisation of macromolecules – particularly large glycosylated systems used in the food, biopharma and healthcare industries. The range or polydispersity of molecular weights and conformations presents special challenges compared to proteins. The review is aimed, without going into any great theoretical or methodological depth, to help the Industrial Biotechnologist choose the appropriate methodology or combination of methodologies for providing the detail he/she needs for particular applications.     

Biodegradation and sorption properties of polydisperse acrylate polymers

Polyacrylate (PA), which is widely used in disposable diapers, is synthesized by polymerization and cross-linking of acrylate. During the synthesis, 3–6% of the polyacrylate polymers is not incorporated into the absorbent material, but remains soluble. If the soluble PA is mobilized from a landfill, it could enter the groundwater. Therefore, the biodegradation and adsorption properties of soluble polymers contained in PA are determined in this study. The soluble PA is highly polydisperse, and the fraction tested has a weight-average molecular-weight of 16,700 and a range extending from 10³ to 10⁵. Sand-column tracer tests show that about 1% of the polyacrylate is unadsorbed, but the remainder has a retardation factor that averages at least 58. Biodegradation kinetics are determined in completely mixed biofilm reactors having a methanogenic consortium grown on glucose. The polyacrylate fraction, as well as glucose and acrylate, are removed and mineralized to CO₂. The Monod parameters for the polyacrylate are: maximum specific rate of substrate utilization = 0.0016 gC/g biomass-day, and half-maximum-rate concentration = 0.79 gC/m³. Although these kinetics are much slower than for glucose and acrylate, significant degradation and mineralization are observed.     

Biological fate of a polydisperse acrylate polymer in anaerobic sand-medium transport

Soluble polyacrylate (PA), a polydisperse mixture of polyacrylate polymers, is strongly adsorbed and biodegradable. Biotic fate studies were carried out with once-through columns containing sand colonized with anaerobic biomass previously grown in a methanogenic fluidized bed. A fraction of soluble PA having a weight-average molecular weight of 16,700 and a range of molecular weight from 10³ to 10⁵ was biologically removed and mineralized to CO₂. Due to its polydisperse nature, the breakthrough curve had a gradual increase to an apparent steady-state removal of approximately 60% near one day when the liquid detention time was 21 minutes. Modeling successfully explained the observed breakthrough result when the fraction was divided into components having a wide range of retardation factors (R): about 25% was strongly adsorbed (R=200 and 500), 45% was moderately adsorbed (R=50 and 100), and 30% was weakly adsorbed (R=1–10). In this study, in which active biomass already was present from utilization of a primary substrate (glucose here), equilibrium adsorption increased the time to breakthrough, which also reduced the exiting concentration by increasing the substrate contact time.     

Conformation of polydispersed chains grafted on nanoparticles

The conformations of polydispersed polymer chains grafted on nanoparticles (NPs) are investigated by coarse-grained molecular dynamics simulations. Combined with the geometric and steric features, we find that most results can be understood by analysing the excluded volume interaction condition of the accommodated chains. By controlling suitable NP size and grafting density, as well as designing a suitable route for preparing the grafted chains with controllable polydispersity and length, it is possible to obtain polymer chains with various conformations, which may be greatly helpful for improving the dispersion of the grafted NPs in the polymer matrix. These results shed light on improved designs of grafted NPs and a better control of dispersion in polymer matrices for promoting the performance of polymer nanocomposite materials.